Integration with TFRecords and created tests

bob/learn/__init__.py

bob/learn/tensorflow/datashuffler/TFRecord.py

bob/learn/tensorflow/loss/BaseLoss.py

bob/learn/tensorflow/loss/__init__.py

bob/learn/tensorflow/script/compute_statistics.py

bob/learn/tensorflow/test/test_cnn.py

bob/learn/tensorflow/test/test_cnn_prefetch.py

bob/learn/tensorflow/test/test_cnn_pretrained_model.py

bob/learn/tensorflow/test/test_cnn_scratch.py

bob/learn/tensorflow/test/test_dnn.py

bob/learn/tensorflow/test/test_inception.py

bob/learn/tensorflow/test/test_layers.py

bob/learn/tensorflow/trainers/SiameseTrainer.py

bob/learn/tensorflow/trainers/Trainer.py

bob/learn/tensorflow/trainers/TripletTrainer.py